Microstrip transmission lines are frequently used as bases for microwave circuits. These lines comprise one or more flat conductors that are separated from a ground plane by an insulating dielectric or substrate. An important advantage of microstrip transmission lines is their relatively low cost since the circuits can be made by etched circuit techniques. Another important advantage is their structural rigidity, which provides circuit stability in the face of external forces. Furthermore, by varying the lengths, widths, and shapes of the conductors, and by proper positioning of adjacent conductors, discrete components such as capacitors, inductors and couplers can be formed out of microstrip transmission line segments.
Currently, however, there are limitations to the use of microstrip transmission lines. Discrete components, such as diodes, are difficult to shunt to microstrip circuits. It has been necessary to mount the component on a pedestal and place the resulting subassembly in a bored-out section of dielectric in which the ground plane is exposed from above. The subassembly is then secured in the bore so that the diode is in electrical contact with the conductor and the pedestal is in electrical contact with the underlying ground plane.
Furthermore, a sizeable amount of electromagnetic radiation may be propagated or received by a component mounted according to this system. This is significant because inductive coupling between adjacent microwave components, caused by the emission and reception of electromagnetic radiation, may adversely affect the operating characteristics of the individual components. The only way to eliminate the inductive coupling is to electrically isolate the individual components. Often the only way to do this is to distance the components away from each other. This makes it difficult to provide a miniaturized circuit on the microstrip.
Also, it is often desirable to integrate different dielectric materials into a single circuit. For example, with a microstrip circuit having a ceramic dielectric, it may be desirable in short sections of the circuit to take advantage of the different characteristics of material such as fused quartz, plastic, beryllium oxide, or other dielectrics. Previously, it has proved difficult to provide a microwave circuit with more than one type of insulating dielectric. When it has been necessary to provide a circuit with more than one dielectric, a separate circuit would have to be provided for each dielectric.
Furthermore, it is sometimes necessary to provide a microwave circuit with more than one type of transmission line. For example, it may be desirable to provide a circuit composed primarily of microstrip, with short lengths of coaxial line or stripline, which are other forms of microwave transmission lines. Currently, there is no convenient way to provide an integrated circuit having more than one type of transmision line. When it is necessary to use more than one type of transmission line, more than the one circuit must be used.
Also, it is often desirable to connect a microwave circuit to other circuits in order to assemble a complete electronic device. Often these connections are made by way of coaxial cables. It is then necessary to provide coaxial feed-through connectors between the microwave circuits and the cables to which they are connected. Since these feed-throughs are separate components, they have their own inductive coupling characteristics that affect the operation of the circuits. Furthermore, it is costly to electrically connect a feed-through to a circuit, and to mechanically connect it to a circuit's housing.
Additionally, it is sometimes desirable to provide a conventional, non-microwave, circuit, such as one made with a printed wire board, with one or more microwave components. At the present it is difficult to mount such components to such a circuit because the electromagnetic radiation they receive and propagate affects the operation of the entire circuit. As a result it is necessary to mount any microwave components that are part of a conventional circuit to a separate circuit board so they are electrically isolated from the nearby components.
A need therefore exists for a new electrical circuit interconnection system so that components can be readily connected to a microstrip circuit. The system should allow for the components to be readily connected to both the conductor and the ground plane. The interconnection system should also provide a sufficient degree of electrical isolation so the effects of inductive coupling will be minimal. Alternatively, the system should provide total electrical isolation of components so as to eliminate all inductive coupling between adjacent components. This would provide a means for integrally mounting a set of microwave components to a conventional circuit.
Furthermore, the system should allow for sections with different dielectrics, or sections of different types of transmission lines to be connected to the basic stripline microwave circuit. The interconnection system should also make it possible to readily connect a coaxial feed-through connector to a microstrip circuit so that it is an integral part of the circuit.